Resonant absorption reducing device



May 12, 1942. D. v. SINNINGER RESONANT ABSORPTION REDUCING DEVICE Filed April 26, 1939 fwujzm ATTORNEY Patented May 12, 1942 RESONAN T ABSORPTION REDUCING DEVICE Dwight V. Sinninger, Chicago, 111., assignor to Johnson Laboratories, Inc.,

poration of Illinois Chicago, 111., a cor- Application April 26, 1939, Serial No. 270,193

4 Claims. This invention relates to high-frequency signaling systems, and more particularly to multiple-band coil systems for use in radio receivers.

Radio receivers which are intended to cover more than one range of signal frequencies usually employ a plurality of inductance coils and switching means to selectively connect the proper group of coils into the variably tuned resonant circuits of the receiver for the reception of signals in each of the respective ranges covered. The receiver may be tuned to resonance with the desired signal by inductance or capacitance variation, or by a combination of both, and my invention is applicable to each of these general methods. The use of my invention is especially advantageous, however, in inductively tuned systems having movable ferromagnetic cores for varying the circuit inductances. This method of operation is known as permeability tuning.

A variable inductance device suitable for this purpose is disclosed by Polydoroff in United States Patent No. 1,940,228, in which a resonant circuit is tuned by a movable ferromagnetic core of relatively large diameter and short axial length. An improved form of such a device is disclosed by Schaper in United States Patent No. 2,051,012, in which the diameter of the movable ferromagnetic core is relatively small compared with its axial length. Both Polydoroifs original system and Schapers improved system readily cover an adequate range of frequencies and may easily be ganged to provide multiple-unit systems.

In a permeability-tuned multi-range receiver, the inductance coils for each stage are conveniently arranged coaxially and a single core arranged to pass through them in succession, the proper coil being connected into circuit by a suitable switch, so that the circuit is tuned first through one range of frequencies and then through a second range by continuous movement of the core. This general system is shown and described by my co-workers Kirk, Jacob and Mc- Ginley in their United States patent application Serial No. 197,222, filed March 21, 1938, Patent No. 2,226,822 issued December 31, 1940, which is directed primarily at the mechanical aspects of such a multiple-range tuning system.

When inductance coils are mounted coaxially in a multiple-range receiver, and particularly when the coupling between them is increased by the presence of a ferromagnetic core, difiiculty is experienced due to resonant absorption effects. This is most noticeable by the presence of dead spots in the high-frequency tuning range because of the absorption by the resonant circuits which are formed in the low-frequency inductance coil due to its distributed capacitance. This absorption may be serious enough to prohibit satisfactory reception of one or more signals in the high-frequency range which the receiver is designed to cover, This problem is discussed in Penders Electrical Engineers Handbook, volume V, 1936, pages 4-24 and 4-25, where it is stated that absorption may be eliminated by short-circuiting adjacent coils or coil sections, not in use, or by placing a shielding short-circuited turn between adjacent coils. These efforts are not entirely successful in eliminating the interference, and the short-circuited turns, absorbing some energy, diminish the Q of the active circuit. The most effective shielding is gained by the use of separate coils each separately shielded, which of course makes for a more bulky and expensive circuit.

It is an object of my invention to provide an inexpensive and compact inductance coil assembly for use in multiple-range receivers, which is substantially free from undesired absorption effects between the respective coils.

An additional object of my invention is to so Wind one of the coils of a multiple coil assembly as to substantially eliminate its effect upon adjacent coils, without resorting to shielding or other undesirable expedients.

A further object of my invention is to provide an inductance coil in which resonances due to distributed capacitance are of substantially reduced magnitude.

These and other objects are realized, in accordance with my invention, by employing an inductance coil having an interlace of small distributed capacitances of relatively high power factor. In such a coil, numerous small resonant circuits are formed, but they are of low efliciency and hence do not have a serious absorption effeet. The presence of these small resonant circuits does not have an appreciably detrimental effect upon the performance of the coil at the frequencies at which it is intended to operate, since the external capacitor with which it is used has a relatively large capacitance value and a relatively very low power factor. Furthermore, instead of there being a few resonances of a high order of magnitude within the coil, there are a great number of overlapping resonances having negligible absorption at any one frequency. This is due to couplings which are beyond critical, so that the resonant peaks are separated and lower than would be the case at lower degrees of coupling.

The invention will be better understood by reference to the drawing, in which:

Fig. 1 shows in elevation an inductance device embodying the invention;

Fig. 2 shows the method of winding one of the coils of the device of Fig. 1; and

Fig. 3 is the wiring diagram of a portion of a radio receiver incorporating the inductance device of Fig. 1.

Referring to Fig. 1 of the drawing, inductance coils I and 2, slightly axially spaced, are wound on insulating tube 3, which has an internal diameter such as to slidably support ferromagnetic core 4. Coils I and 2 each have an axial length approximately equal to that of core 4. Any suitable actuating means, as for example cable 5 and pulleys 6, may be provided for moving core 4 axially with respect to coils I and 2. Coil I is Wound with a relatively large total number of turns, but only a very few turns are applied during each cross of the Winding feed and the turns of successive layers are in oblique relation. The winding is of the universal type, but considerably elongated compared with the conventional universal coil. Thus the total distributed capacitance of the coil is relatively high, but the high value is due to the large number of small capacitances which are produced by this method of winding rather than to a few large capacitanccs as is usually the case. Coil 2, on the other hand, is an ordinary spaced-turn solenoidal winding having relatively few turns and very low distributed capacitance.

The method of winding coil I will be more readily apparent from Fig. 2 of the drawing, which shows only the first two layers of this coil in place of form 3. As is apparent from this figure, only a very few turns are applied as the winding progresses from right to left and the same number of turns during the return from. left to right. The beginning of each of the turns is indicated by a letter, the alphabetical sequence of the letters corresponding with the order in which the turns are applied. There are numerous capacitances between closely adjacent turns, as for example between turns a and h, b and g, c and f, and so forth, but the losses in each of these capacitances are relatively small because the potential differences within the respective pairs of turns are a very small portion of the total potential difference existing between the terminals of coil I.

Fig. 8 shows the use of the inductance device of Fig. 1 in the preselector of a radio receiver.

Antenna I is connected through primary winding 8 and resistor 9 to ground. The low-potential terminals of coils I and 2 are connected through capacitor I to the ungrounded terminal of resister 0, and to ground through capacitor II. The high-potential terminals of coils l and 2 are connected to ground through adjustable capacitors I2 and I3, respectively, and are each connected to one terminal of single-pole doublethrow switch It, the arm of which is connected to control-grid I of vacuum tube I6. Cathode H of vacuum tube It is grounded throu h resistor I8 shunted by capacitor I9. Direct-current bias voltage is supplied to control-grid I5 from any suitable source through resistor 20. Vacuum tube It is the first tube of a radio receiver or the like, and may function either as an amplifier or otherwise, for example as the first detector of a superheterodyne radio receiver, without atfecting the mode of operation of the invention.

In operation, inductance coil I and capacitor equal success.

I2 are connected into circuit by means of switch I4 for reception of signals in the lower-frequency range, as for example the broadcast range from 540 to 1725 kilocycles, and inductance coil 2 and capacitor I3 are similarly employed for reception of signal frequencies in the higher frequency range, as for example 5.9 to 18.0 megacycles. The circuit is initially adjusted for resonance at a desired frequency at the high-frequency end of each tuning range by means of capacitors l2 and i3, respectively, and is tuned over each range by movement of core 4 with respect to the corresponding inductance coil. Although the coils are mounted coaxially and closely adjacent each other, the absorption effects of the lowerirequency coil during use of the higher-frequency coil are negligible, as explained above.

In one successful embodiment of the invention in accordance with Figs. 1 and 3, inductance coils I and 2 each have an axial length of 1.6875 inches, and they are separated by 0.1875 inch. Insulating tube 3 has an outside diameter of 0.332 inch and an inside diameter of 0.316 inch. Ferromagnetic core 4 has a diameter of 0.3125 inch and a length of 1.8% inches. Coil I comprises 220 turns of No. 36 double silk enamelled wire, wound with four turns per cross. This coil has an air-core inductance of 84:.0 microhenries at 1000 cycles per second, and a total distributed capacitance of 34 micromicrofarads. Coil I is intended for use in the frequency range of 540 to 1725 kilocycles. Coil 2 comprises 33 turns of No. 36 enamelled wire and has a 1000- cycle inductance of 3.4 microhenries. This coil is intended to cover a range of signal frequencies from 5.9 to 18.0 megacycles. Primary winding 8 comprises t .ree turns. Resistors 9 and 20 have resistances of 15,000 ohms and 0.5 megohm, re-

spectively. Capacitors I0 and I I have capacitances of 0.01 and 0.001 micromicrofarad, respectively.

It will be understood that, by suitable choice of constants, an inductance device in accordance with the invention may be employed equally well between a high-frequency amplifying vacuum tube and the following vacuum tube, or in the oscillator circuit of a superheterodyne radio receiver.

It will also be understood that where the ex pression coil diameter is used in this specification and the appended claims, reference is made to the mean diameter of the winding itself. If a multilayer winding is employed, for example, the coil diameter as used herein would refer to the mean diameter of the several layers of the winding. In this specification and the appended claims, the term layer is understood to mean that portion of the winding which is applied during a single one-way crossing of the winding feed.

Although the invention is particularly useful in radio receivers, it will be understood that it is not limited to such use, but may be employed in other types of high-frequency apparatus with These and other modifications which will occur to those skilled in the art are within the scope of my invention.

Having thus described my invention, what I claim is:

1. A tuning unit for a radio receiver to provide two continuously tunable ranges of higher and lower frequencies respectively, including two coaxially and adjacently disposed windings each of a length several times its diameter, and a ferromagnetic core arranged to be movable into one or the other of said windings, the winding for the range of higher frequencies being a solenoidal winding and the other winding comprising a plurality of angularly displaced and parallel traverses having equal small numbers of widelyspaced turns, the arrangement being such that any parallel and closely adjacent turns belong to different traverses.

2. A tuning unit for a radio receiver to provide two continuously tunable ranges of higher and lower frequencies respectively, including a singlelayer solenoidal winding for the higher of said frequency ranges, a second winding disposed coaxially with and adjacent to said first winding and having a length several times its diameter for the lower of said frequency ranges, a ferromagnetic core disposed Within said windings, means for moving said core axially of and into one or the other of said windings, and a switch for connecting one or the other of said windings to an appropriate capacitance to form resonant circuits tunable by motion of said core over a higher or lower frequency range respectively, said second winding having a plurality of angularly displaced and parallel traverses having equal small numbers of widely-spaced turns the arrangement being such that any parallel and closely adjacent turns belong to different traverses.

3. A tuning unit for a radio receiver to provide two continuously tunable ranges of higher and lower frequencies respectively, including a single-layer solenoidal winding for the higher of said frequency ranges, a second winding disposed coaxially with and adjacent to said first winding and having a length several times its diameter for the lower of said frequency ranges, a ferromagnetic core disposed within said windings, means for moving said core axially of and into one or the other of said windings, and a switch for connecting one or the other of said windings to an appropriate capacitance to form resonant circuits tunable by motion of said core over a higher or lower frequency range respectively, said second winding having a plurality of angularly displaced traverses wound back and forth axially of said winding, said traverses having equal small numbers of widely-spaced turns and starting and ending in the same starting and ending planes, the number and spacing of the turns in each traverse being such that the turns of the back and forth traverses intersect at an oblique angle.

4. A tuning unit for a radio receiver to provide two continuously tunable ranges of higher and lower frequencies respectively, including a long thin-walled insulating tube, a single-layer spaced-turn solenoidal winding from about the center toward one end of said tube for the higher of said frequency ranges, a second winding from about the center of said tube toward the opposite end thereof for the lower of said frequency ranges, a cylindrical ferromagnetic core of a diameter slightly less than the internal diameter of said tube slidably disposed within said tube, each of said windings and said core being of approximately the same length, means for moving said core axially of and into one or the other of said windings, and a switch for connecting one or the other of said windings to an appropriate capacitance to form resonant circuits tunable by motion of said core over a higher or lower frequency range respectively, said second winding having a number of angularly displaced traverses wound back and forth axially of said tube, said traverses having equal small numbers of widely-spaced turns and starting and ending in the same starting and ending planes, the number and spacing of the turns in each traverse being such that the turns of the back and forth traverses intersect at an oblique angle.

DWIGHT V. SINNINGER. 

